Fuel cell power plants normally include fuel gas steam reformers which are operable to catalytically convert a fuel gas, such as natural gas, into hydrogen, carbon monoxide and carbon dioxide. The conversion involves passing a mixture of the fuel gas and steam through a catalytic bed which is heated to a reforming temperature of about 1,250.degree. F. to about 1,600.degree. F. Catalysts typically used are nickel catalysts which are deposited on alumina pellets. A typical reformer will consist of a plurality of reaction tubes which are contained in a housing that is insulated for heat retention. The reaction tubes are heated by burning excess fuel gas in the housing and passing the burner gasses over the reaction tubes. The individual reaction tubes will typically include a central exhaust passage surrounded by an annular entry passage. The entry passage is filled with the catalyzed alumina pellets, and a fuel gas-steam manifold is operable to deliver the fuel gas-steam mixture to the bottom of each of the entry passages whereupon the fuel gas-steam mixture flows through the catalyst beds. The resultant heated hydrogen, carbon monoxide, carbon dioxide and remaining stream gas mixture then flows through the central exhaust passages in each tube so as to assist in heating the inner portions of each of the annular catalyst beds; and thence from the reformer for further processing and utilization.
Steam reformers require a large catalyst bed surface area in order to provide a high degree of catalyst-fuel mixture interaction and a large heat transfer surface area to produce the amount of hydrogen required to operate the fuel cells at peak efficiency. This need for large catalyst bed and heat transfer surface area, when met by using catalyst-coated pellets in tubular reformers, results in undesirably large and heavy reformer assemblies. For example, a commercially available 200 KW acid fuel cell power plant includes a steam reformer component which has a volume of about 150 to 175 cubic feet; and weighs about 3,500 lbs.
My International Patent Application No. WO 97/24176, published Jul. 10, 1997, discloses an improved steam reformer structure which provides the necessary catalyzed and heat transfer surface area, is substantially smaller and lighter than presently available steam reformers, and can be operated at lower service temperatures. The improved steam reformer structure is formed from a series of essentially flat plate reformer components. Each of the reformer components includes reformer passages which are adjacent to a plurality of central regenerator/heat exchanger passages. Each of the reformer passage plate units is disposed directly adjacent to a burner passage plate unit so that the adjacent reformer and burner passages share a common wall.
All of the metal sheets which make up the flat plate reformer and some of the burner components of the assemblage may have surfaces covered with a catalyzed alumina coating. The surfaces to be catalyzed will be primed by means of a conventional wash coating process such as that provided by W. R. Grace and Co., or Engelhard Corp., for example. By washcoating the fuel gas passage walls in the reformer with a catalyzed and stabilized alumina composite; and in certain cases, washcoating the burner passages with a stabilized, catalyzed, or non-catalyzed, composite, the operating efficiency of the reformer assemblage can be enhanced.